Spring is astir in the usual ways in St. Paul. Songbirds are chirping, tulips are emerging, and the hot mix asphalt plant is cranking away again.

For the 50th time in as many years, the now-rickety plant in the Frogtown neighborhood, which opens each March, is heartening street crews -- and motorists -- around the region, because the "hot mix" the plant cranks out is better at patching potholes than anything that's available in the winter.

"It's worth our while to take an hour in the morning to drive down and get the good stuff," said Mark Thompson, street superintendent in Elk River, one of many cities around southeastern Minnesota that buy asphalt from St. Paul.

Like Girl Scout cookies and maple syrup, St. Paul's hot mix asphalt is symbolic of winter's end. The "cold mix" that's available in winter is only a temporary fix for the potholes that plague city streets. Hot mix bonds better to the surrounding pavement; its availability means smoother streets are on their way, even after a mild winter like this one.

'It's always fresh'

On a recent cool but sunny morning, a steady stream of trucks from Elk River, Anoka, Northfield and other cities lined up under a hopper at the city-owned and -operated St. Paul plant. Huge doses of 335-degree black asphalt dropped into their boxes, shrouding the trucks and the plant with steam. The St. Paul plant can make about 200 tons of asphalt an hour, and it has to be applied the day it's made, while it's still pliable.

There is likely to be less call for pothole remedies this year, after a couple of really bumpy spring thaws. The formula for a bad pothole year includes a wet fall and a snowy winter, but the Twin Cities has received only about half its normal precipitation since August.

"One of the essential ingredients to creating a pothole is water getting into the pavement, then into the sub-base," said Anoka County Engineer Doug Fischer. "So the fact that our pavements have been so dry coming into the winter and pretty much all winter long has been a great benefit."

In a bad year, melting snow and ice leach through cracks in the pavement into the sub-base. Fluctuating warm and freezing temperatures cause the water to expand and contract, pushing and pulling the asphalt with it. The road surface eventually crumbles from the exertion.

In that way, warmer-than-average weather also has played into smoother rides this spring.

In Minneapolis, where crews reconstructed or refurbished 45.3 miles of streets last year, the city received 80 pothole complaints from Feb. 6 to March 12, compared with 917 during the same period in 2011. Mike Kennedy, Minneapolis' director of transportation maintenance and repair, said the city has seen a real benefit from the reconditioned roads as well as the warmer, drier weather.

50th birthday

Still, through thick and not-so-thick on the pothole front, the St. Paul plant has soldiered on since opening in 1962, replacing a plant built 50 years before.

Workers still gauge the volume of material in hoppers by pulling on ropes, like church bell-ringers, and control the mix of aggregate and hot oil at a panel of buttons and levers in a tiny, elevated control room, where the key recipes are written on a small piece of note paper stuck to a plexiglass window.

The plant has survived in sort of Goldilocks fashion. It's big enough so that other communities don't have to have their own, but small enough to stay out of competition with big commercial operations. It produces just enough material to meet demand for early-season patching before the large producers, whose asphalt goes into big paving projects, get up and running for the season. St. Paul brought in $3.6 million in asphalt sales in 2011, up from $3.1 million the year before.

Minneapolis had its own asphalt plant until the mid-1990s, when a decades-long citywide street upgrade ended, reducing its need for asphalt, and the plant itself needed too many repairs, said public works Director Steve Kottke. Minneapolis now buys its early-season hot mix from St. Paul.

The St. Paul plant -- reminiscent of both a grain elevator and the Millennium Falcon of "Star Wars" -- isn't pretty, but street maintenance supervisor Chris Anderson, also in his 50th spring, said it has aged well.

"It's very popular, particularly in the spring," he said. "It's our baby. It's a beautiful thing."

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